This invention relates to a cooling unit for acoustic devices a typical example of which is a power amplifier, and more particular to a cooling unit for acoustic devices which can effectively suppress noises produced by a cooling fan.
Recently, acoustic devices have been improved not only in performance but also in output, and high power amplifiers are provided with a cooling fan as forcible cooling means. This tendency is significant with acoustic devices installed on vehicles.
For instance, as shown in FIG. 1, in order to cool a power amplifer 1, an electric motor 2 for driving a cooling fan is connected to a cooling fan circuit 3 having a cooling fan drive power source 3A, and the input terminal 1A of the power amplifier 1 is connected to the output terminal of a reproducing device (or player) or the like whereas the output terminal 1B is connected to a loudspeaker 4. Thus, during operation of the power amplifier, the cooling fan driven by the motor 2 supplies cooling air to the power amplifier 1 to cool the latter.
In the above-described cooling unit, the cooling fan is operated independently of the level of the input or output signal of the power amplifier 1; in other words, the cooling fan supplies air to the power amplifier 1 at a certain flow rate corresponding to the maximum amount of heat generated by the power amplifier 1 to cool the latter 1. Therefore, when the output level is low for instance in the case where the operation of the music source is suspended or the reproduction comes between pieces of music, or a pause period occurs in the reproduction, the air cutting sound or vibration of the cooling fan becomes conspicuous inside the vehicle, thus causing the operator to feel disagreeable with it.